The subject invention relates to (1) pigment dispersants, (2) their use in pigment dispersions containing pigment and liquid carrier and (3) coating compositions containing the pigment dispersions. The dispersants are useful in the manufacture of a wide variety of pigmented resin-containing coating compositions.
Pigmented coating compositions are useful for their aesthetic as well as protective features. Such compositions contain a film-forming resin and a pigment dispersed in a liquid carrier. It is important that the pigment be satisfactorily dispersed throughout any film which results from the application of the coating composition. It is therefore desirable that the pigment be well dispersed throughout the liquid coating composition. Typically, the pigment to be used in a coating composition is first dispersed with only a portion of the total film-forming resin of which the coating composition is comprised together with appropriate liquid carriers and additives. The resulting dispersion is then mixed with the remainder of the film-forming resin and any other necessary components to produce the coating composition. Most pigment dispersants are very specific in their performance and are compatible with only a small number of the diverse solvents and film-forming resins used in coating compositions. For example, in the case of an acrylic resin based coating composition, the pigment will be first dispersed with a portion of the acrylic resin in the presence of an organic solvent. The resultant product is then further diluted with the remainder of the acrylic resin and any other necessary components forming a part of the coating composition. The final color of the coating composition is normally adjusted by small further additions of pigment dispersions containing the same or similar film-forming resins just prior to use. This further addition is normally referred to as "tinting".
A number of different film-forming resins are used in the manufacture of different coating compositions. Accordingly, heretofore it has been necessary to predisperse pigments with a portion of the film-forming resin or a resin compatible therewith, which is appropriate to each type of coating composition. That is, even though the pigmentation of two coating compositions containing different film-forming resins may be identical, it has been necessary to disperse each pigment or mixture of pigments separately with the appropriate film-forming resin. This is necessary so as to avoid any problems of incompatibility in the final coating composition. In a similar manner any tinting operation requires the use of dispersants which are compatible with the film-forming resin being used.
One solution to the aforementioned well-known problem has been the development of so-called "multi-purpose" pigment grinding vehicles. The polymeric dispersants contained in the multi-purpose pigment grinding vehicles are compatible with a wide range of film-forming resins and solvents. It can readily be recognized that a pigment grinding vehicle which can be used in many coating systems would be of significant savings to the coatings industry. Thus, one set of pigment dispersions could be used with a wide variety of coating compositions.
There have now been found dispersants based on the polymerization products of specific monomeric units which are capable of acting as multi-purpose dispersants. Such dispersants are useful for dispersing pigments and which can then be used in resin-containing coating compositions.
As used herein all percentages and ratios are by weight unless otherwise indicated.